This invention relates to methods and apparatus for forming dynamo-electric machine stators of the type that are made by helically coiling a longitudinal strip of ferro-magnetic material.
Barrera U.S. Pat. No. 4,512,376 and Cardini et al. U.S. Pat. No. 5,845,392 (both of which are hereby incorporated by reference herein in their entireties) show apparatus for applying coils of wire to stator cores to produce stators that are particularly useful for making alternators. It is known to produce this type of stator core by helically coiling a strip of ferro-magnetic material to produce a hollow cylinder. The strip is provided with transverse recesses spaced from one another along one of the strip""s longitudinal edges. The spacing of the recesses and the helical coiling are such that recesses in successive turns of the coil become superimposed on one another. In this way the superimposed recesses produce slots in the stator core that extend parallel to the longitudinal axis of the hollow cylinder and that are spaced from one another in the circumferential direction around the inside of the hollow cylinder. These slots receive the coils of wire that were mentioned earlier.
The electrical efficiency and thus performance of stators of a given size of the type described above can be improved by making them from thinner strip material. However, to make a stator core of a given size from thinner material either takes longer or requires the stator core forming machinery to operate faster, both of which are undesirable. For example, to make a stator forming machine operate faster increases its cost and may also increase the rate of wear of the machine. More machine cycles may be required to produce stators of a given size using thinner strip material, and therefore the number of stator cores that can be produced during the useful life of a machine may decrease when thinner strip material is used.
It is also known that the strip material used to produce the stator cores can have variations in thickness, metallurgical and mechanical properties, and geometrical configuration. These variations can lead to undesirable variations in the diameter of the internal surface of the helical stator core. Variations in the internal surface affect the performance of the helical stator core. These variations in the strip material can occur between reels of strip material and throughout a reel of strip material. There are also local variations or deformations that can occur at particular isolated points on the strip material. It has been found that these local variations can disrupt the electromagnetic flow within fabricated stator cores and thus hinder the performance of the stators.
Stator cores can also be made by combining two helically formed strips from separate stator forming machines each using a different reel of strip material. Additional advantages can be achieved by combining the two helically formed strips with an additional lamination inserted between the two helically formed strips. The two helically formed strips and lamination are combined by aligning their longitudinal axes and the recesses of each piece. Differences in the internal diameter of the two helically formed strips are not desirable.
Strip material that is helically coiled undergoes deformation. Depending on the dimensions and properties of the strip material, additional unwanted deformations may occur. One factor which affects the occurrence of unwanted deformations is the thickness of the strip material. Typically, the thinner the strip material, the more likely unwanted deformations will occur.
In view of the foregoing, it is an object of this invention to provide improved methods and apparatus for making dynamo-electric machine stator cores.
It is a more particular object of this invention to provide methods and apparatus for making stator cores from thinner strip material, which methods and apparatus avoid the need to operate the stator forming machinery either longer or faster to produce stator cores of a given size.
It is also an object of this invention to provide methods and apparatus for reducing the effect of variations that can occur in the strip material on the electrical performance of the stator cores. More specifically, the performance can be increased by reducing the variations that can occur in the internal diameter of stator cores and by reducing the effects of local variations that may be present in the strip material.
It is another object of this invention to provide methods and apparatus for reducing unwanted deformations that can occur when strip material is coiled.
These and other objects of the invention are accomplished in accordance with the principles of the invention by providing methods and apparatus in which, in at least some embodiments, two relatively thin strips of stator core material are superimposed on one another to form a composite strip before the composite strip is helically coiled to produce the hollow cylinder of the stator core. In this way each strip can be half as thick as the single strip used previously, but the machinery can operate at the same speed to produce finished stator cores of a given size at the same rate as the prior art machinery.
The methods and apparatus of at least some embodiments of the invention typically include superimposing the two strips so that recesses in those strips are superimposed on one another to produce recesses in the composite strip. The composite strip is coiled so that recesses in successive turns of the coil are superimposed on one another to produce slots for receiving wire coils as in prior art stators. The methods and apparatus of the invention may include shaping (e.g., punching) each of the strips to produce the above-mentioned recesses. The methods and apparatus of the invention may also include periodically severing the coil from the composite strip to produce end faces of the stator cores. The methods and apparatus of the invention may still further include axially compressing the coils (e.g., to square off the ends of the stator core) and welding the compressed coils together to rigidify the structure. The methods and apparatus of the invention may also include selectively pressure rolling the strips in order to achieve a more constant internal diameter of the stator core. The internal diameter of the stator core can also be measured in order to provide feedback to adjust the pressure rolling.
Another aspect of at least some embodiments of the invention includes applying the principles of selective pressure rolling to alternative methods and apparatus for forming dynamo-electric machine stator cores in which the stator cores are fabricated by combining two helically formed strips from separate stator forming machines that include selectively pressure rolling the strips.
An additional aspect of at least some embodiments of the invention includes coiling strip material that contains apertures within the strip to reduce unwanted deformations.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.